Habitat Use of Everglades Fishes in Relation to Seasonal Hydrology: Implications for Wading Bird Prey Availability Mark I. Cook Everglades Systems Assessment, SFWMD Jennifer S. Rehage, Greg Hill Earth & Environment, SERC, FIU
Everglades Trophic Hypothesis Local-scale environment Nutrient levels Microtopography Large fish population size Local-scale environment Hydrology (e.g. depth, recession rates, Frequency of drying Days since drydown) Periphyton standing stock/ composition Regional-scale environment Vegetation structure Landscape configuration Prey population size Prey responses Prey availability (dry season prey concentrations) Habitat selection, food intake, foraging aggregations Nesting effort and productivity Population size Wading bird responses
Everglades Trophic Hypothesis Local-scale environment Nutrient levels Microtopography Large fish population size Local-scale environment Hydrology (e.g. depth, recession rates, Frequency of drying Days since drydown) Periphyton standing stock/ composition Regional-scale environment Vegetation structure Landscape configuration Prey population size Prey responses Prey availability (dry season prey concentrations) Habitat selection, food intake, foraging aggregations Nesting effort and productivity Population size Wading bird responses
How is prey availability influenced by the fine-scale movement and habitat selection decisions of individuals?
Objectives To understand the fine-scale movements and habitat choices of key prey species in relation to seasonal hydrology and other factors. 2014 Study: Warmouth Lepomis gulosus Q1: How are Warmouth distributed across ridge and slough habitats? Q2: How are these distribution patterns influenced by seasonal hydrology? Q3: How do unseasonal reversals in the drying pattern affect distribution patterns?
S O U T H F L O R I D A W A T E R M A N A G E M E N T D I S T R I C T Methods: Field Enclosures & Passive Detection at LILA
Methods: Field Enclosures & Passive Tagging at LILA
S O U T H F L O R I D A W A T E R M A N A G E M E N T D I S T R I C T Methods: Field Enclosures & Passive Tagging at LILA Warmouth Lepomis gulosus
Example of Movement: Tag detections for a given individual over 24 hrs (See Rehage et al. (2014) Acta Ethologica)
Data collection in 2014 Tracked 36 tagged warmouth in 6 enclosures Encompassed the seasonal drydown & rewetting period (115 d from Mar 8 June 30) Experimentally raised water-levels (25 cm) for 15 days in early May
Warmouth favored deeper habitats but their distribution was strongly influenced by hydrological period Habitat effect: p = 0.001 Hydrological period x habitat: p = 0.0001
Distributions in relation to seasonal changes in water depth
Seasonal Drydown: Maximum use of the gator hole occurred when the slough was relatively deep (~15 cm) Ridge: minimal & declining use to ~8 cm Slough: moderate & constant use, then a rapid decline in use between 25 15 cm Gator hole: greatest use after slough drops to ~15 cm
Experimental and seasonal reversals: Fish rapidly vacated deeper habitats and moved to newly re-flooded habitats Ridge Slough Alligator hole
Experimental and seasonal reversals: Fish rapidly vacate deeper habitats and move to newly re-flooded habitats Ridge Slough Alligator hole
The relationship between habitat use and water depth was habitat specific, nonlinear and varied in strength r 2 = 0.69 r 2 = 0.88 r 2 = 0.18 r 2 = 0.90 r 2 = 0.07 Segmented regressions
Summary Warmouth primarily use deeper habitat but alter distributions rapidly (daily scale) as water levels rise and fall with seasonality. Responses to water level may be non-linear, habitat specific, threshold dependent. Max densities of warmouth (concentration events) occur in the deepest habitats when the slough is still relatively deep (~15 cm). Water level reversals cause fish to move to recently reflooded habitats (loss of concentration) Effects of reversals on fish movements may vary Warmouth can potentially re-concentrate
Thanks to: Eric Cline, Fred Sklar, Amartya Saha, Nate Dorn & the Rehage lab Funded by: SFWMD & RECOVER